The present disclosure relates to a sheet post-processing device that staples a sheet sheaf and to an image forming apparatus.
It is generally known that paper sheets on which an image has been formed is ejected and stacked on an exit tray. It is also known that the exit tray is elevated and lowered according to the height of the stack of paper sheets.
In one example, a disclosed paper ejecting device detects the height of a stack of paper sheets on an exit tray using an arm that touches a top surface of the stack of paper sheets. The paper ejecting device detects a position of the top surface of the stack of paper sheets by detecting a position of a proximal end of the arm.
The paper ejecting device allows even stapled paper sheets to be stacked on the exit tray in an aligned manner.